This invention relates to barrier films and methods of making the barrier films. More particularly, the invention relates to (1) barrier films comprised of a flexible polymeric substrate and an amorphous carbon coating and (2) methods of making the barrier films using a gas plasma coating technique.
Barrier films are well known and widely used. They are extensively used in packaging for protecting a food item from the deleterious effects of oxygen and water vapor. Barrier films are also used in other commercial and industrial applications where a low degree of permeability to some extent is needed. Such films are made of a variety of materials and composite materials. For example, single layers of aluminum foil and Saran (trademark of the Dow Chemcial Company) are two household barrier films which are economical and capable of acting as a barrier to the migration of oxygen or water vapor. Coated materials such as waxed paper are useful household barrier films which are economical and capable of providing a measure of low oxygen and water vapor permeability.
Carbonaceous materials have been suggested in the prior art as capable of providing a coating having properties making them desirable for certain applications. Amorphous carbon coatings, in particular have been reported to be hard, optically transparent, non-conductive to electricity, and resistant to acids and alkalis. They have been used for the coating of optical lenses and as protective films in abrasive applications. See for example, U.S. Pat. Nos. 4,060,660; 4,382,100; and 4,504,519. However, the use of such coatings have not been suggested for use in barrier films.
The above noted barrier film coated materials are made by a variety of techniques. The particular coating technique used is primarily based on the substrate and coating material and the type and degree of physical properties needed in the final product. That is, certain coating techniques are more capable of producing coatings which are free of surface defects which could affect the coating's appearance and physical properties.
While the known barrier films are acceptable, there is still a need for barrier films with even better physical properties and better economics of production. In particular, there is a need for a barrier film having a low oxygen permeability rate. Such a film would also be optically transparent for appearance purposes and have physical properties which would make it suitable as a packaging material.